This invention relates to a line concentrator for use between a highway for a time division data switching exchange and a plurality of asynchronous and synchronous data terminals which send out and receive asynchronous and synchronous data signals. The line concentrator as called herein may also serve as a line distributor as the expression is used elsewhere, for example, in U.S. Pat. No. 3,862,370 issued Jan. 21, 1975, to Shinsuke Kadota, assignor to Nippon Electric Company, Limited, one of the present assignees. The highway may either be an interoffice or an intra-office highway.
It is generally necessary on supplying data and/or speech signals to a time division switching exchange to resort to a multiplexer for sampling the signals sent from a plurality of terminals into a time division multiplexed signal train. On distributing a time division multiplexed signal train from such a switching exchange to terminals, it is necessary to use a demultiplexer which is usually called by the name of multiplexer. For asynchronous and synchronous data signals, the samples have been subjected before transmittal thereof to the highway to bit processing described hereinafter with reference to the accompanying drawing. On the other hand, a PCM switching exchange is preferred in view of its capability of dealing with PCM telephone signals which may be deemed herein as some of the synchronous data signals and in consideration of a future PCM integrated communication system. Also, envelope interleaving is preferred to bit interleaving in view of CCITT Recommendation X.21 while (6 + 2)-bit envelope, with a six-bit character plus F and S bits, has already been standardized as a result of the proposal made in CCITT Recommendation X.50 dated May, 1972. Under the circumstances, envelope interleaving is preferred although bit interleaving may result in shorter frame length and in a simpler channel structure.